Voltage Management in Unbalanced Low Voltage Networks Using a Decoupled Phase- Tap-Changer Transformer

Transcription

1 Downloded from orit.dtu.dk on: Jul 5, 28 Voltge Mngement in Unlned Low Voltge Networks Using Deoupled Phse- Tp-Chnger Trnsformer Coppo, Mssimilino ; Turri, Roerto ; Mrinelli, Mtti; Hn, Xue Pulished in: Proeedings of Interntionl Universities' Power Engineering Conferene (UPEC) 24 Link to rtile, DOI:.9/UPEC Pulition dte: 24 Link k to DTU Orit Cittion (APA): Coppo, M., Turri, R., Mrinelli, M., & Hn, X. (24). Voltge Mngement in Unlned Low Voltge Networks Using Deoupled Phse-Tp-Chnger Trnsformer. In Proeedings of Interntionl Universities' Power Engineering Conferene (UPEC) 24 [693489] IEEE. DOI:.9/UPEC Generl rights Copyright nd morl rights for the pulitions mde essile in the puli portl re retined y the uthors nd/or other opyright owners nd it is ondition of essing pulitions tht users reognise nd ide y the legl requirements ssoited with these rights. Users my downlod nd print one opy of ny pulition from the puli portl for the purpose of privte study or reserh. You my not further distriute the mteril or use it for ny profit-mking tivity or ommeril gin You my freely distriute the URL identifying the pulition in the puli portl If you elieve tht this doument rehes opyright plese ontt us providing detils, nd we will remove ess to the work immeditely nd investigte your lim.

2 Voltge Mngement in Unlned Low Voltge Networks Using Deoupled Phse-Tp-Chnger Trnsformer Mssimilino Coppo, Roerto Turri Deprtment of Industril Engineering University of Pdov, Itly Mtti Mrinelli, Xue Hn Deprtment of Eletril Engineering (CEE) DTU- Tehnil University of Denmrk Astrt The pper studies medium voltge-low voltge trnsformer with deoupled on lod tp hnger pility on eh phse. The overll ojetive is the evlution of the potentil enefits on low voltge network of suh possiility. A relisti Dnish low voltge network is used for the nlysis. The lod profiles re hrterized y using single phse mesurement dt on voltges, urrents nd tive powers with minutes resolution. Different senrios re onsidered: no tp tion, three-phse oordinted tp tion, single phse disrete step nd single phse ontinuous tp tion. The effetiveness of the tpping pility is evluted y ompring the Voltge Unlne Ftor nd the voltge levels on the neutrl le. Index Terms Distriuted Genertion, Automti Voltge Control, Power Trnsformer, Smrt Grids I. INTRODUCTION Mny reent projets envisged the possiility to modulte the energy onsumption in LV networks y modulting the feeding voltge of the end-users [], [2]. This pproh, known s CVR (Conservtion Voltge Redution), is suitle for networks with three-phse users, therefore with lned voltge on the three phses. However, the inresing presene of Distriuted Energy Resoures (DERs) like photovolti nd new storge-ple lods (e.g., plug-in hyrid eletri vehiles), my result into non-monotoni voltge vritions long the feeder, whih my tully e mitigted y proper mngement of retive power provision of smll photovolti genertors [3] or eletri vehiles [4]. The effets of different ontrol strtegies for three-phse inverter-onneted DG-units on voltge unlne in distriution networks hve een presented in [5] to study oth the voltge negtive-nd zero sequene omponents. Furthermore, sine LV networks host oth single nd three-phse users, the different power flow on the phses my result into some voltge unlne issues tht n interfere with voltge ontrol strtegy (i.e. CVR). The prolem of network regultion in unlned onditions is ddressed in [6], [7] nd [8] where different ontrol strtegies of emedded three nd four wire inverters re presented. A solution for the voltge onditioning in LV networks is presented onsidering n on-lod-tp-hnging (OLTC) opertion of the seondry susttion trnsformer. Some ommeril produts re lredy ville for the sope relying on eletroni swithing pility [9] nd re ommonly known s smrt trnsformers []. The novelty of the proposed pproh is the mngement of voltge unlnes deoupling the tp vrition mong the phses. It mens tht in se one of the phse voltges is prtiulrly loded, the trnsformer will redue the rtio just on tht speifi phse, without involving onfigurtion hnges of the other two phses. The methodology dopted in this study is desried in Setion II long with the modelling pproh used for the OLTC phse-wise trnsformer. Severl senrios re defined in Setion III long with the relevnt informtion of rel LV Dnish network. The results re presented in Setion IV nd the finl remrks nd future studies re reported in Setion V. A. Prolem sttement II. METHODOLOGY It is ommon in Denmrk to hve three phses onnetion ville even for reltively smll residentil users nd, depending on the lyout of the household eletril instlltion, onurrent lods my e onentrted on just one phse. Moreover, the inresing presene of smll single phse distriuted energy resoures (DER) like photovolti nd new storge-ple lods (e.g., plug-in hyrid eletri vehiles), is leding into unorrelted voltge vritions long the feeder: it my hppen tht one phse voltge is inresing long the feeder, while the others re deresing. Therefore, sine LV networks host oth single nd threephse prosumers, the different power flow on the phses my

3 led to voltge unlnes tht n interfere with the CVR ontrol strtegy. The novelty of the proposed pproh is the utiliztion of deoupled OLTC MV/LV trnsformer, whih is ple of regulting eh single phse tp hnger in different wy. A reserh projet imed t the reliztion of this kind of trnsformer is reently strted nd will foresee the testing on the experimentl fility SYSLAB of the Risø DTU nd future pplition on the field. The present work ims t providing, y evluting hievements in term of voltge unlnes nd losses redution on LV feeder, fesiility nlysis of n OLTC distriution trnsformer with deoupled tp pility. The tp hngers n regulte the single phse voltge ±5% the nominl vlue. B. Multi-Phse system modeling In order to perform the nlysis in LV distriution network, power flow tool le to del with symmetril systems is needed. The method dopted for this work hs een lssified s Current Injetion method nd llows rrying out power flow nlysis on multi-phse systems [2]. The priniple leding to the omposition of the potentilly symmetril system is depited in Fig. where the Network Admittne Mtrix is omposed strting from the rnhes definition (self nd mutul dmittnes) inluding lines nd trnsformers. The system is then integrted with the shunt elements (whether they re lods or genertors) whih re represented s prllel of onstnt dmittnes nd vrile urrent injetors, so the totl urrent ontriution depends on oth terms nd gives the possiility to hnge the models voltge dependeny. Fig.. System representtion for the symmetril power flow nlysis. Shunt elements re onneted to the externl ports (red). Erth onnetion dmittnes my lso e onsidered s externl elements (green). A similr pproh is lso dopted in the softwre OpenDSS relesed y EPRI [3] used in this work to ompute the simultions presented in setion IV. C. Trnsformer modeling Y network Y rnh Y rnh 2 Yrnh n One the network model is uilt s for the sheme depited in Fig. 2, the trnsformer needs to e represented s n dmittne mtrix onneting the PCC (LV usr) to the MV network. The lssil pproh used defining the trnsmission mtrix of generi single-phse trnsformer [4] is implemented to onsider eh phse s primitive mtrix. Sine for this work ontrol on the single phses ws needed in order to independently ontrol the trnsformer rtios, the model is uilt y three single-phse trnsformers, eh seondry side onneted etween n erthed neutrl point nd different phse of the LV grid, wheres t the primry side (MV usr) the onnetion is mde etween two phses, s for the Delt onnetion, resulting in three-phse Delt-Wye trnsformer model, s shown in Fig. 2. E A E B E C E D Fig. 2. Three phse Delt-wye trnsformer model. Fig. 2 shows shemti representtion of the trnsformer model: in prtiulr it n e notied tht, sine the MV side works with isolted neutrl, the fourth port is open, while t the seondry side the neutrl point is onneted to the reltive ondutor in the four-wire system. Furthermore, for this pper it hs een onsidered tht eh phse of the LV side hs the possiility to perform tp-hnging tion, onditioning the reltive phse voltge independently. III. NETWORK LAYOUT AND TESTING SCENARIOS A. Dnish low voltge network m m 2 m 3 E E E E d The network onsidered for pplition onsists in 2- us Dnish LV feeder onneted to the MV network through /.4 kv trnsformer s shown in Fig. 3 [5]. The short iruit power of the min network is 2 MVA. Mesurements on the rel system llowed hrterizing the power onsumption of the 33 single phse lods during 24-hours intervl whih resulted to e out 74 kwh, with men power of 3.8 kw. The totl energy nd men power mounts for eh phse re reported in TleTABLE I. The three-phse trnsformer is modeled s desried in Setion III enling the phse-wise independent opertion of the proposed OLTC. TABLE I. TOTAL LOAD ENERGY (24 HOURS) AND MEAN POWER VALUE. Phse Phse Phse Energy [kwh] Men Power [kw]

4 Bus Bus4 Bus6 MV usr LV usr Bus2 Bus5 PCC Bus3 Fig. 3. Single line digrm of the Dnish network. Controlled Bus Time (h) Fig. 4. Ative power input on the three phses. Overll sum for the 33 single phse lods. Power (kvar) Power (kw) phses Phse Phse Phse 3 phses Phse Phse Phse Time (h) Fig. 5. Retive power input on the three phses. Overll sum for the 33 single phse lods. Ative power overll lod input Retive power overll lod input B. Simultion senrios The defined senrios im t investigting the effets of the OLTC instlled t the MV/LV Susttion. In prtiulr, n nlysis of the feeder-end phse voltges is mde in order to evlute the voltge mgnitude nd voltge unlne level under different operting onditions. Strting from the Bse Cse Senrio, derived from the voltge nd urrents mesurements on the rel system, three other senrios re presented to evlute the possile effets of the ontrol:. Synhronized OLTC: the OLTC is operted simultneously on the three phses, tking s referene the phse voltge t phse. The tphnging rtio is the sme dopted for off-lod opertion in distriution trnsformers; 2. Phse-wise OLTC disrete: three independent ontrollers re set referring eh one to one phse of the system. The ontrol uses the sme tp hnging rtio used for the synhronized tion; 3. Phse-wise OLTC ontinuous: the independent tion of eh phse is onsidered with higher numer of tps with smller vritions. The OLTC ontrollers operte t the MV/LV trnsformer seondry usr, using s input vrile the voltge t the ontrolled us (Bus 6 in Fig. 3) in eh phse with the ojetive to minimize the voltge devition with respet to referene voltge V ref, here set to pu. The ontrol onsiders non-tion zone round the mentioned referene voltge (lled Ded-Bnd), in this work set t ±2% V ref, with the possiility to swith on 5 positions for totl ±5% Vn vrition, i.e. with steps of V=2.5% Vn. A more urte regultion n e hieved with finer ontrol of the OLTC, mintining the voltge vrition rnge t ±5% Vn while reduing the step voltge vrition V t.% Vn with Ded-Bnd set t ±.25% Vn. MV network sign( x ) n tp = n tp = PCC n yes OLTC OLTC OLTC LV network Ded - Bnd V > 2 Controlled Bus V mesures Fig. 6. Setup of the proposed ontrol strtegy. The OLTC ontrol is shown in detil for one phse. The Ded-Bnd here is intended s the totl rnge (i.e. 4% in senrios A nd B,.5% in senrio C). no V - V ref + V

5 IV. SIMULATION RESULTS C. Bse Cse Senrio - no OLTC The phse-neutrl voltge profile over the 24 hour time period onsidered s Bse Cse for simultions is shown in Fig. 7. As it n e seen, the profile follows wht is expeted in residentil re, with low loding during the night (from to 6.m.) nd higher sorption y lods in the evening (from 6 to 2 p.m.). The mximum voltge sg ould e oserved round 8 p.m. in phse, with.955 pu. Voltge [pu] Phse Phse Phse E. Senrio B: Phse-wise OLTC disrete In the seond senrio, the phse-wise opertion y the OLTC is dopted. In this se the voltge mesurements t the ontrolled us re onsidered individully to perform the independent ontrol on the three phses. For the ske of omprison, the steps rtio nd totl rnge for the OLTC re kept s for the previous senrio. Fig. 9 shows the voltge profile during the 24 hours simultion t us 6 with the phse-wise OLTC ontrol. As it n e seen, the tp ontrollers ret to the Ded-Bnd overoming y the reltive voltge in different instnts reduing the devitions within the Ded-Bnd, ut this opertion ould possily dversely ffet the voltge unlne s shown in Fig., where the Voltge Unlne Ftor (negtive sequene) is evluted in senrios A nd B s for the expression () [6]: Vnegtive seq VUF % = () V positive seq.95 Fig. 7. Voltge t us 6 during the 24 hours period D. Senrio A: Synhronous OLTC The first senrio onsiders the synhronous opertion of the tp-hnger ontrollers on the three phses. The hypothesis is tht the OLTC uses s input vrile the voltge mesurement on one of the phses (in this se phse ). Fig. 8 shows the voltge profile on the ontrolled us with the synhronous tp-hnge opertion t the MV/LV trnsformer. It n e seen tht the ontroller uses V=.25 pu vrition (tp +) when the phse voltge t us 6 overomes the lower threshold.98 pu. When the power onsumption y lods inreses, t round 8 p.m., the tp ontroller swithes to +2 ( V=.5 pu) using voltge rise on the other phses too. Voltge [pu] Phse Phse Phse.95 Fig. 8. Phse voltge t the ontrolled us with synhronous tp hnge y MV/LV OLTC Voltge [pu] Phse Phse Phse.95 Fig. 9. Bus6 phse voltge with phse-wise opertion y MV/LV OLTC. V neg / V pos [%] No reg OLTC synhronized OLTC phse-wise Fig. Comprison etween the unlne in Synhronized nd Phse-wise OLTC ontrols. From the simultions it lerly emerges tht, while synhronous opertion of the OLTC does not ffet the unlne level, the negtive sequene ontent inreses sensily when the OLTC ontroller sets different positions on the phses. This effet is minly given y the disreteness of

6 the ontrol, hving tps whih use voltge vrition of.25 pu eh. F. Senrio C: Phse-wise OLTC ontinuous A signifint improvement in the ontrol ould e given y higher numer of steps, pursuing regultion s lose to ontinuous s possile. In prtiulr, the higher preision of the ontrol enles to redue the Ded-Bnd rehing more urte voltge regultion t Bus6 usr. Fig. shows the result in terms of phse voltges otinle setting the Ded- Bnd width t.5% Vn. In this se the ontrol is more effetive, ontining the mximum devitions round.25% Vn. In Fig. 2 omprison etween the unlne in the disrete nd ontinuous ontrol is mde, stressing the ft tht disrete ontrol with less seletive voltge vrition my worsen the unlne ondition, while ontinuous regultion my result not only in n overll voltge mgnitude improvement, ut lso in smller unlnes. Voltge [pu] Phse Phse Phse V [p.u.],5, Phse Phse Phse Fig. 3. Voltge vrition y phse s for the Senrio C OLTC ontrol. In Tle TABLE II the results disussed so fr re summrized in terms of men vlues. TABLE II. MEAN VALUES FOR THE VUF AND PHASE VOLTAGES IN THE SIMULATED SITUATIONS VUF % Bus 6 Voltge Phse Phse Phse Bse Cse Synhronized Disrete Phse-wise Continuous Phse-wise Fig.. Phse voltge t us 6 with ontinuous OLTC opertion. V neg / V pos [%] No reg Disrete Continuous Fig. 2. Comprison of the VUF with the Disrete nd Continuous OLTC ontrol. In Fig. 3 the voltge vrition imposed y the OLTC on eh phse in senrio C is shown. It lerly ppers tht the ontroller follows the voltge devitions t us 6 operting to mintin the voltge within the ssigned Ded-Bnd. Finlly in Fig. 4 the neutrl potentil t the ontrolled usr is shown for eh senrio. It ould e seen tht in ll three situtions the neutrl potentil is quite similr, just slightly higher in senrio C. This tendeny is justified y the ft tht the voltge vrition otined does not indue sensile vrition on the phse urrents; s onsequene the voltge drop on the neutrl ondutor remins nerly the sme. Neutrl Potentil [pu] Bse Cse Senrio A Senrio B Senrio C Fig. 4. Neutrl potentil t us Bus6 under the different senrios.

7 V. CONCLUSIONS AND FUTURE WORKS This pper fouses on the possiility to ontrol the LV distriution networks voltge through n On Lod Tp Chnger t the Seondry Susttion Trnsformer. Dt nd mesurements on Dnish LV feeder hve een used in 24-hour time simultions in order to ssess the possile effets of this kind of ontrol on rel system. The three senrios onsidered different fetures deling with progressive levels of disretiztion on the voltge ontrol. The results in terms of phse voltge mgnitude nd unlne highlighted the ft tht the phse-wise opertion of the OLTC lthough providing etter ontrol on the overll voltge devitions, my lso result in n unlne worsening when pplying disrete tp hnge with lrge steps. The ontinuous opertion of the OLTC my insted result in etter ontrol improving the voltge qulity on oth the mgnitude nd unlne stndpoints. The results indite tht phse-wise OLTC lthough reduing the voltge devitions does not sort ny effet on the neutrl ondutor potentil. Some improvements in tht sense my ome from n tive mngement of the power exhnge y the users. The ojetive of future works is to extend the simultions nlysis over longer time period (weeks) nd to nlyse the influene of renewle soures, suh s smll three-phse nd single-phse photovolti genertors, on the on lod tp hnging strtegy. During 25, the studied trnsformer will e tested in the experimentl fility SYSLAB-PowerL.DK of the DTU Risø Cmpus. VI. AKNOWLEDGEMENTS This work hs een prtly funded y the Energy Sving y Voltge Mngement Projet (EUDP Dnish projet). The uthors thnk for the useful disussions the tem of PSS Energy Group A/S nd DONG Energy nd thnk Dr. Junjie Hu for the help in prepring the input dt. REFERENCES [] K.P. Shneider, F.K. Tuffner, J.C. Fuller nd R. Singh, Evlution of Conservtion Voltge Redution (CVR) on Ntionl Level, Pifi Northwest Ntionl Lortory, July 2 [2] S. Rhimi, M. Mrinelli nd F. Silvestro, Evlution of requirements for Volt/Vr ontrol nd optimiztion funtion in distriution mngement systems, Energy Conferene nd Exhiition (ENERGYCON), 22 IEEE Interntionl, pp , Florene, 9-2 Sept. 22. [3] F. Adinolfi, F.Bino, M. Mrinelli, S. Mssuo, nd F. Silvestro, Model of rel medium voltge distriution network for nlysis of distriuted genertion penetrtion in SmrtGrid senrio, Innovtive Smrt Grid Tehnologies (ISGT Europe), 22 3rd IEEE PES Interntionl Conferene nd Exhiition on, pp.-7, Berlin, 4-7 Ot. 22. [4] L. Crrdore, nd R. Turri, Eletri Vehiles prtiiption in distriution network voltge regultion, Universities Power Engineering Conferene (UPEC), 2 45th Interntionl, pp.-6, Crdiff, 3 Aug. - 3 Sept. 2. [5] B. Meersmn, B. Renders, L. Degroote, T. Vndoorn, nd L. Vndevelde, Three-phse inverter-onneted DG-units nd voltge unlne, Eletri Power Systems Reserh, Volume 8, Issue 4, April 2, Pges [6] R. Cldon, M. Coppo, R. Turri, Coordinted Voltge Control in MV nd LV Distriution Networks with Inverter-Interfed Users, in: Pro. IEEE Powerteh 23, Grenole, 6-2 June 23 [7] R. Cldon, M. Coppo, R. Turri, Distriuted voltge ontrol strtegy for LV networks with inverter-interfed genertors, Eletri Power Systems Reserh, Volume 7, Ferury 24, Pges 85-92, ISSN: , doi:.6/j.epsr , 24 [8] W. Sinsukthvorn, E. Ortjohnn, A. Mohd, N. Hmsi nd D. Morton, "Control Strtegy for Three-/Four-Wire-Inverter-Bsed Distriuted Genertion," IEEE Trnstions on Industril Eletronis, vol. 59, no., pp , Ot. 22. [9] FITformer REG. Tehnil Brohure. [Online] [] W. Willems, T.L. Vndoorn, J.D.M. De Kooning, L. Vndevelde, Development of smrt trnsformer to ontrol the power exhnge of mirogrid, Innovtive Smrt Grid Tehnologies Europe (ISGT EUROPE), 23 4th IEEE/PES, pp.-5, Copenhgen, 6-9 Ot. 23. [] CIGRÉ Tsk Fore C6.4.2, Benhmrk Systems for Network Integrtion of Renewle nd Distriuted Energy Resoures, CIGRÉ report, 29. [2] K. Sunderlnd, M. Coppo, M.F. Conlon nd R. Turri, Applition of orretion urrent injetion power flow lgorithm to n unlned 4- wire distriution network inorporting TN-C-S erthing, in Pro. 48 th Universities' Power Engineering Conferene (UPEC 23), pp. -6, Dulin, 2-5 Sept. 23. [3] OpenDSS wesite: ww.eletridss.soureforge.net [4] G. Andersson, Modelling nd Anlysis of Eletri Power Systems, ITET ETH Zurih, Mrh 23. [5] X. Hn, S. You, F. Thordrson, D.V. Tkie, S.M. Osterg, O. Pedersen, H.W. Bindner, nd N.C. Nordentoft, Rel-time mesurements nd their effets on stte estimtion of distriution power system, Innovtive Smrt Grid Tehnologies Europe (ISGT EUROPE), 23 4 th IEEE/PES, pp.-5, Copenhgen, 6-9 Ot. 23 [6] P. Pilly e M. Mnyge, "Definitions of voltge unlne, IEEE Power Engineering Review, pp. 5-5, My 2.